Introduction

Cor triatriatum is a rare condition occurring when a child is born with a thin, fibro-muscular membrane subdividing either the left or the right atrium into 3 chambers. The condition is also classified as a congenital heart defect. Cor triatriatum sinister is the most common form. The left atrium divides via an atrial appendage into an upper and a lower chamber. The upper chamber receives blood from the pulmonary veins, while the lower chamber is attached to the left atrial appendage blocking the mitral valve orifice creating a significant left ventricular inflow obstruction. The presence of the left atrial appendage differentiates cor triatriatum from another congenital heart defect, supravalvular mitral stenosis.[1]

Another, rarer form of cor triatriatum is cor triatriatum dextrum. With cor triatriatum dextrum the right valve of the sinus venosus persists dividing right atrium into 2 chambers. This form presents similarly to Ebstein's anomaly and is difficult to differentiate.

Etiology

Cor triatriatum results from the incomplete absorption of the common pulmonary vein, which is normally reabsorbed during the development of a fetus and becomes a part of the left atrium. The incomplete absorption results in the formation of an appendage which subdivides the left atrium into 2 chambers. No known genetic mutations or risk factors are found to be associated with the development of this condition.

Epidemiology

Cor triatriatum presents in association with other congenital cardiac defects such as tetralogy of Fallot, atrial septal defect, ventricular septal defect partial anomalous pulmonary venous connection, and represents only 0.1% to 0.4% of all congenital abnormalities.[2] The membrane may be complete or may contain one or more fenestrations of differing size.

Pathophysiology

A malincorporation theory[3] presented by Dr. Clifford G. Parsons explains how cor triatriatum sinister occurs. During normal fetal development, the pulmonary vein incorporates into the left atrium. If it fails to do so, the common pulmonary venous ostium remains narrow, resulting in a septum-like structure called the atrial appendage. The appendage then further divides the left atrium into 2 compartments. Although widely accepted, this theory fails to explain how fossa ovalis and atrial muscle fibers are also present in the proximal atrial chamber.[4]

Two other theories, malseptation theory and entrapment theory, also explain the pathophysiology of cor triatriatum. The malseptation theory states that the fibro-muscular membrane is an abnormal growth of the septum primum; whereas, entrapment theory emphasizes the entrapment of the common pulmonary vein in the embryonic sinus venosus, thereby preventing its incorporation into the left atrium. The malincorporation theory remains the most widely accepted theory.

History and Physical

Classically, cor triatriatum presents in infancy with signs and symptom of pulmonary hypertension and pulmonary venous obstruction. Due to low cardiac output, children can show poor growth and weight gain, feeding difficulties, respiratory distress, and tet spells. In childhood and adulthood, the signs and symptoms of pulmonary venous hypertension and right heart failure dominate as the membrane calcifies, and the opening becomes smaller and smaller decreasing cardiac output even further. Mitral valve regurgitation and atrial fibrillation impose serious dangers. Most patients present with the following features[5]:

Dyspnea and orthopnea

Easy fatigability

Hemoptysis

Exercise intolerance and shortness of breath

Palpitations

Atrial fibrillation can cause systemic thromboembolism and present as pulmonary embolism or stroke. The left atrial enlarges due to backing up of blood and can present as life-threatening arrhythmias.

Cor triatriatum sinister that presents for the first time in adulthood is rare but possible. It presents similarly to mitral stenosis, but the absence of loud S1 and an opening snap helps to distinguish between the 2. Chest x-ray showing pulmonary congestion with an absence of left atrial enlargement is characteristic of cor triatriatum. A continuous gradient on Doppler echocardiography confirms the diagnosis.[4][6]

Physical Exam

The physical exam findings are due to the right heart failure and pulmonary congestion.

Accentuated pulmonary component of second heart sound

A soft mid-systolic murmur at the upper left sternal border with a wide and fixed splitting of an atrial septal defect.

Right ventricular heave

Rales at the lung base

Diminished peripheral pulses

Hepatomegaly and right upper quadrant tenderness

Ascites

Peripheral edema

Distended peripheral veins

Distended jugular venous and elevated jugular venous pressure

Pallor

Poor weight gain

Evaluation

The mainstay of evaluation and diagnosis includes imaging studies such as chest x-ray, ECG and echocardiography, angiography and left and right heart catheterization.[7][8]

Chest X-Ray

A chest x-ray is the initial investigation of choice. The findings include:

Pulmonary congestion with haziness (Kerley B-lines)

Ground glass appearance of acute pulmonary edema

Prominent pulmonary vessels

Pleural effusion

Left atrial enlargement

Cardiomegaly

Electrocardiography (ECG)

ECG findings are non-specific in cor triatriatum. Can range from atrial fibrillation and no specific P-wave changes to right axis deviation due to pulmonary congestion and right ventricular hypertrophy.

Echocardiography

Echocardiography is the diagnostic modality of choice as it not only allows for definitive diagnosis, but the 3-dimensional reconstruction of echocardiographic images pinpoints the exact location of the defect and appendage, helps direct the surgical approach to the disease. The left atrial appendage and its fenestrations can be easily visualized along with the presence of an atrial septal defect, pulmonary stenosis, mitral valve stenosis, or regurgitation. Pulmonary arterial and venous drainage patterns can also be seen on echocardiography. Echocardiography differentiates between cor triatriatum and supravalvular mitral stenosis by clear visualization of the left atrial appendage in the left atrium.

Transesophageal echocardiography outlines the precise nature and anatomy of the defect; especially in older patients, but if unavailable, transthoracic echocardiography can be performed. [9][10]

Angiography

Angiography helps determine the severity of obstruction and the time of surgical intervention needed.

Treatment / Management

Medical Management

Asymptomatic Patients

Asymptomatic patients need no specific treatment. Observe the patients for the development of signs and symptoms. Schedule regular medical follow-ups.

Surgery is the definitive treatment. Complete surgical resection of atrial appendage/accessory membrane through a midline sternotomy under cardiopulmonary bypass and closure of atrial septum with a pericardial patch provides the optimum cure. The 10-year survival rate following surgery is 83%, while patients with coexisting congenital heart diseases have a greater risk of adverse outcomes and a lower survival rate.[11][12]

Differential Diagnosis

Many congenital heart diseases can present similarly to cor triatriatum and should be taken into consideration when making a diagnosis of this disorder. These include:

Supravalvular mitral stenosis

Mitral stenosis

Idiopathic pediatric pulmonary arterial hypertension

Pulmonary venous hypertension

Total anomalous pulmonary venous return

Partial anomalous pulmonary venous return

Atrial septal defect/ ventricular septal defect

Ventricular septal defect

Idiopathic pulmonary hypertension

Tricuspid stenosis

Atrial myxoma

An experienced surgical team should evaluate imaging results as high suspicion can accelerate diagnosis and delay or prevent unfavorable outcomes.

Complications

Right-sided failure

Pulmonary edema/hypertension

Atrial arrhythmias

Death

Deterrence and Patient Education

Pediatric cardiologist

Pediatric cardiac surgeon

Intensivist

Enhancing Healthcare Team Outcomes

Cor-triatriatum is a very rare congenital heart disorder. However, most infants are symptomatic at birth and need neonatal intensive care unit (NICU) care. Nurses play a vital role in the monitoring of these infants both pre and post surgery. The infants need to be monitored for arrhythmias, pulmonary edema, or right heart failure. The outcomes for untreated infants is poor. The outcomes for other infants with cor triatriatum depend on the presence of other co-existing heart defects. For those with only the cor triatriatum defect, the outcomes are excellent. The surgery is best done at centers with experience with this disorder. While it appears that only the accessory membrane needs to be resected, the small size of the left atrium and collapse of the structure during cardiopulmonary bypass can make visualization difficult.[11][13]

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A 4-year-old girl presents to the emergency department with shortness of breath, fever, and cough. She also complains of fatigue on exertion, tachypnea, and that her fingers turn blue when she runs about a mile. She has a history of recurrent hospitalizations due to respiratory tract infections. After a thorough examination, the diagnosis of congenital heart disease is suspected. Which of the following will confirm the diagnosis of cor triatriatum in this child?

Echocardiography showing the presence of an accessory membrane in the right ventricle

Echocardiography showing the presence of a fibro-muscular membrane with fenestration in the left atrium

Left heart catheterization showing blockage at the level of the left anterior descending artery

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